Various flavor mixing and dispensing devices have heretofore been made for mixing a flavoring material with a neutral frozen confection such as ice cream, frozen custard or the like to produce a flavored frozen confection. Some prior devices such as shown in U.S. Pat. Nos. 2,262,293; 2,736,534, 3,224,740; and 3,830,407 utilized a mixing and dispensing device having a single mixing chamber and a single rotary mixer connected to the outlet of a frozen confection freezer, and with a selector valve arrangement which enabled introduction of a selected one of a plurality of different flavoring materials into the mixing chamber for a mixture therein with the frozen confection to produce a flavored frozen confection. Such prior devices, however, were not entirely satisfactory because of flavor carry-over when changing from one flavoring material to another. A volume of mixed product containing the neutral frozen confection and a flavoring material remained in the mixing chamber at the completion of a dispensing operation and, when the dispenser was changed to dispense material of a different flavor, the volume of mixed material that remained in the mixing compartment from the previous dispensing operation, was discharged during the initial portion of a subsequent dispensing operation. Some flavoring materials such as chocolate are very strong and only a small amount of such flavoring materials can adversely affect the flavor of the mixed product, when dispensing a different flavor. U.S. Pat. No. 3,830,407 recognizes this problem and suggests, as a means of limiting contamination, that one of the inlet tubes to the mixing chamber be interconnected with a source of water such that the dispensing nozzle can be flushed before a different flavor is dispensed.
In order to avoid the problems of flavor carry-over, it has also been proposed as disclosed in U.S. Pat. Nos. 3,276,633; 3,934,427 and 3,934,759, to use a plurality of mixing chambers, one for each flavor to be dispensed with a separate mixer in each mixing chamber. Use of multiple mixing chambers and mixers not only increases the cost of producing the multiple flavor mixing and dispensing device, but also markedly complicates the time and trouble encountered in cleaning the mixing and dispensing apparatus.
U.S. Pat. No. 4,378,164 discloses a dispensing unit for ice cream machines in which a selected one of a plurality of different flavoring materials is introduced into the periphery of a rotor that is disposed just above a star shaped extrusion port so that the flavoring material is carried into the ice cream primarily through the radial slits of the star shaped extrusion port to be located primarily on the portion of the ice cream that passes through the outer portions of the radial slits. The dispensing unit of this patent is not arranged to uniformly intermix the flavoring material with the neutral frozen confection to produce a flavored frozen confection. In order to minimize carry-over of flavor from one dispensing operation to the next, the patent suggests that the electrically operated flavor control valves be deenergized at the end of each dispensing operation a little in advance with respect to the ice cream admission to the cylinder, so that the last amount of ice cream delivered will eliminate flavoring syrup from the dispenser. However, in order to achieve substantially uniform mixing of the flavoring material in the frozen confection as the materials pass from their inlet ports to the discharge outlet, it is necessary to provide a mixing chamber having a relatively large volume. It would accordingly be necessary to pass a relatively large volume of frozen confection through the mixing chamber, after shut-off of the flavoring material, to purge substantially all of the flavored frozen confection from the mixing chamber.